1. Field of the Invention
The present invention relates to a display device. The invention more particularly relates to an active matrix type display device which is improved in the response speed or the emission efficiency by decreasing the contact resistance in a through-hole.
2. Description of the Related Art
In an organic EL display device or a liquid crystal display device, scanning lines are extended in a first direction and arranged in a second direction. Further, video signal lines are extended in the second direction and arranged in the first direction. Areas surrounded by the scanning lines and the video lines define pixels and a thin film transistor (TFT) is formed for each of the pixels.
The organic EL display device is configured to control current supplied to an organic EL layer by a TFT while the liquid crystal display device is operated to select signals on images supplied to pixel electrodes. The TFT is formed of a-Si or poly-Si.
In the organic EL display device, since the organic EL layer is driven by the current, it is necessary to increase the mobility of a semiconductor constituting the TFT. Further, a small-sized liquid crystal display device is such that a driving circuit is mounted in a liquid crystal display panel. Since high speed operation is necessary for the TFT for the driving circuit, it is necessary to increase the mobility of the semiconductor. Accordingly, a poly-Si TFT is used in the organic EL display device or the small-sized liquid crystal display device.
Generally, to form a poly-Si semiconductor layer, an a-Si semiconductor layer is first formed and then excimer laser is radiated to the a-Si semiconductor laser to convert a-Si into poly-Si. Installation investment is necessary and process control is difficult for the radiation of the excimer laser. In view of this, JP-A-2007-142059 that a semiconductor layer of poly-Si is formed by radiating an a-Si semiconductor layer not by the excimer laser but by light of a lamp.